1. Field of the Invention
The present invention relates to a memory device, and particularly relates to a memory device which performs refreshing.
2. Description of the Related Art
Since DRAM (dynamic random access memory) uses a memory cell constituted of one transistor and one capacitor, it needs periodic refreshing in order to store and retain data. One type of refreshing is performed according to an external refresh command and another type of refreshing is performed such that a memory device internally performs self refreshing automatically.
In Japanese Patent Application Laid-open No. 2001-118383, a DRAM which performs refreshing automatically and does not need an external refresh instruction is described.